1. Field of the Invention
The present invention relates to an electronic flash apparatus and a camera having this electronic flash device.
2. Description of the Related Art
Many recent cameras have an electronic flash device. There are various types of cameras ranging from conventional fixed focus cameras to zoom cameras including a zoom lens. With the lenses of the recent cameras in the tele-side (long focus side of the lens), a distant object can be enlarged for photographing. Further, since the cameras having an electronic flash device have been reduced in size, users can carry these cameras with themselves more easily.
On the other hand, the electronic flash device requires a larger amount of charging energy to provide a proper quantity of light to a more distant object. Moreover, attempts are being made to reduce the size of the cameras and increase zoom magnification. As a result, the F No., which is indicative of the brightness of the lens on the tele-side, has increased (that is, the lens has become darker). This further increases the required amount of charging energy of the electronic flash device.
However, the reduced size of the cameras with the electronic flash device has led to several disadvantages such as a decrease in the total number of batteries (for example, lithium batteries) used as a power supply from two to one, thus reducing the power supply voltage. Further, such batteries have a high internal resistance. As a result, the amount of time required to charge the electronic flash disadvantageously increases.
Thus, there has been a demand for an electronic flash device which can reduce the charging time and a camera having such an electronic flash device.
It is an object of the invention to provide an electronic flash device which reduces the charging time.
It is another object of the invention to provide an electronic flash device which is capable of performing charging operations suitable for manipulating and operating conditions of a camera.
It is a further object of the invention to provide an electronic flash device having a forward type booster circuit and a flyback type booster circuit and being capable of switching these two types of booster circuits to obtain proper charging time and charging efficiency.
To attain the above objects, a first aspect of the present invention provides an electronic flash device comprising a power supply, a main capacitor, a booster circuit for performing a boosting operation for increasing voltage from the power supply to thereby charge the main capacitor, the booster circuit having a forward type boosting section, and a flyback type boosting section, and a switching circuit for switching the boosting operation performed by the booster circuit from one performed by the forward type boosting section to one performed by the flyback type boosting section, during charging of the capacitor.
In a preferred form of the first aspect of the invention, the switching circuit switches the boosting operation performed by the forward type boosting section to the one performed by the flyback type boosting section after a charged voltage of the main capacitor has reached a predetermined value.
Alternatively, the switching circuit switches the boosting operation performed by the forward type boosting section to the one performed by the flyback type boosting section when a predetermined period of time has elapsed since charging of the capacitor was started.
In a preferred form of the first aspect of the invention, the forward type boosting section and the flyback type boosting section share an oscillation transformer connected in parallel to the main capacitor.
In a specific embodiment of the first aspect, the oscillation transformer has a primary coil and a secondary coil, and the forward type boosting section causes a current to flow through the primary coil of the oscillation transformer in a first direction to generate a current flowing from the secondary coil in a predetermined charging direction to thereby charge the main capacitor, and the flyback type boosting section causes a current to flow through the primary coil in a second direction opposite to the first direction to generate a current flowing from the secondary coil in the charging direction to thereby charge the main capacitor.
In a more specific form of this embodiment, the primary coil comprises a first coil, a second coil, and an intermediate terminal connecting between the first and second coils, the power supply having electrodes, the first and second coils being connected to one of the electrodes of the power supply, the intermediate terminal being connected to another one of the electrode of the power supply, and the forward type boosting section causing a current to flow through the first coil in the first direction to generate a current flowing from the secondary coil in the predetermined charging direction to thereby charge the main capacitor, while the flyback type boosting section causing a current to flow through the second coil in the second direction opposite to the first direction to generate a current flowing from the secondary coil in the charging direction to thereby charge the main capacitor.
Alternatively, the forward type boosting section and the flyback type boosting section each have an oscillation transformer connected in parallel to the main capacitor.
To attain the above objects, a second aspect of the present invention provides an electronic flash device incorporated in or mounted on a camera, comprising a power supply, a main capacitor, a booster circuit for performing a boosting operation for increasing voltage from the power supply to thereby charge the main capacitor, the booster circuit having a forward type boosting section, and a flyback type boosting section, and a selecting circuit for selecting the forward type boosting section or the flyback type boosting section depending on an operating status or an operative state of the camera.
In a specific form of the second aspect of the invention, the selecting circuit selects the forward type boosting section when the camera is in an operative state for preparing for photographing, and selects the flyback type boosting section before the camera is set in the operative state for preparing for photographing.
Specifically, for example, the selecting circuit selects the forward type boosting section or the flyback type boosting section depending on an operating state of a release operating member of the camera. For example, the camera is set into the operative state for preparing for photographing by a remote control operation.
To attain the above objects, a third aspect of the present invention provides an electronic flash device incorporated in or mounted on a body of a camera, comprising a main capacitor, a flyback type booster circuit for charging the main capacitor with a driving current which can be variably set, and a control circuit for causing the flyback type booster circuit to charge the main capacitor by setting the driving current from the flyback type booster circuit to a predetermined first value, when the camera is in an operative state for preparing for photographing, and by setting the driving current from the flyback type booster circuit to a predetermined second value which is smaller than the first predetermined value, before the camera is in the operative state for preparing for photographing.
To attain the above objects, a fourth aspect of the present invention provides an electronic flash device incorporated in or mounted on a body of a camera, comprising a main capacitor, a forward type booster circuit for charging the main capacitor, the forward type booster circuit having a first transformer, and a second transformer having a smaller turn ratio than the first transformer, and a control circuit for using the first transformer to charge the main capacitor when the camera is in an operative state for preparing for photographing, and for using the second transformer to charge the main capacitor before the camera is in the operative state for preparing for photographing.
In the third and fourth aspects, the operative state for preparing for photographing is a state in which a release operating member of the camera is operated for a first stroke.
In the third and fourth aspects, the camera may be set into the operative state for preparing for photographing by a remote control operation.
To attain the above objects, a fifth aspect of the present invention provides an electronic flash device comprising a power supply battery, a main capacitor, a booster circuit for performing an oscillating operation for increasing voltage from the power supply battery to thereby charge the main capacitor, the booster circuit having a first boosting section, and a second boosting section using a charging method different from that of the first boosting section, and a control circuit for switching the first boosting section to the second boosting section to charge the main capacitor, the control circuit setting timing for the switching depending on a state of the power supply battery.
To attain the above objects, a sixth aspect of the present invention provides an electronic flash device comprisinga power supply battery, a main capacitor, a booster circuit for performing an oscillating operation for increasing voltage from the power supply to thereby charge the main capacitor, and a control circuit for switching a driving operation of the booster circuit from a first driving operation to a second driving operation which achieves faster charging than the fist driving operation, to charge the main capacitor, the control circuit setting timing for the switching depending on a state of the power supply battery.
In a preferred form of the fifth and sixth aspects, the first boosting section comprises a flyback type boosting section, and the second boosting section comprises a forward type boosting section.
Preferably, the control circuit sets the timing for the switching depending on a state of internal resistance of the power supply battery.
Also preferably, the control circuit sets the timing for the switching based on a time required for charging the main capacitor which is obtained by the state of the power supply battery.
Preferably, the control circuit sets the timing for the switching such that a time required for a charged voltage of the main capacitor to increase up to a predetermined charge completion voltage is substantially constant.
To attain the above objects, a seventh aspect of the present invention provides an electronic flash device incorporated in or mounted on a body of a camera, comprising a main capacitor, a flyback type booster circuit for charging the main capacitor with a driving current which can be variably set, and a control circuit for causing the flyback type booster circuit to charge the main capacitor by setting the driving current from the flyback type booster circuit to a predetermined value when a quick charging mode is set, and by setting the driving current from the flyback type booster circuit to a value smaller than the predetermined value when the quick charging mode is not set.
To attain the above objects, an eighth aspect of the present invention provides an electronic flash device incorporated in or mounted on a body of a camera, comprising a main capacitor, a forward type booster circuit for charging the main capacitor, the forward type booster circuit having a first coil, and a second coil having a smaller turn ratio than the first coil, and a control circuit for causing the forward type booster circuit to charge the main capacitor using the first coil thereof when a quick charging mode is set, and using the second coil thereof when the quick charging mode is not set.
To attain the above objects, a ninth aspect of the present invention provides an electronic flash device incorporated in or mounted on a body of a camera, comprising a main capacitor, a booster circuit having a forward type boosting section, and a flyback type boosting section to be selectively used for charging the main capacitor, and a selecting circuit for selecting the forward type boosting section or the flyback type boosting section depending on a photographing mode of the camera.
To attain the above objects, a tenth aspect of the present invention provides an electronic flash device incorporated in or mounted on a body of a camera, comprising a main capacitor, a flyback type booster circuit for charging the main capacitor with a driving current which can be variably set, and a setting circuit for setting the driving current from the flyback type boosting circuit depending on a photographing mode of the camera.
To attain the above objects, an eleventh aspect of the present invention provides an electronic flash device incorporated in or mounted on a body of a camera, comprising a main capacitor, a forward type booster circuit for charging the main capacitor, the forward type booster circuit having a first coil, and a second coil having a smaller turn ratio than the first coil, and a determining circuit for determining whether to charge the main capacitor using the first coil of the forward type booster circuit or the second coil thereof depending on a photographing mode of the camera.
To attain the above objects, a twelfth aspect of the present invention provides an electronic flash device incorporated in or mounted on a body of a camera having a finder eye contact detecting circuit for detecting an eye contact with a finder, comprising a power supply, a booster circuit for increasing voltage from the power supply to thereby charge the main capacitor, the booster circuit having a first boosting section, and a second boosting section, the second boosting section requiring a shorter charging completion time to complete charging the main capacitor, than sad first boosting section, and the first boosting section having a higher charging efficiency than the second boosting section, and a selecting circuit for selecting the second boosting section when the finder eye contact detecting circuit detects the eye contact with the finder, and selecting the first boosting section when the finder eye contact detecting circuit does not detect the eye contact with the finder.
In a preferred form of the twelfth aspect, the first boosting section comprises a flyback type boosting section, and the second boosting section comprises a forward type boosting section.
Preferably, the finder eye contact detecting circuit detects the eye contact with the finder during charging of the main capacitor using the first boosting section, the selecting circuit switches the first boosting section to the second boosting section.
To attain the above objects, a thirteenth aspect of the present invention provides an electronic flash device incorporated in or mounted on a body of a camera having a finder eye contact detecting circuit for detecting an eye contact with a finder, comprising a power supply, and a control circuit for charging the main capacitor by selecting a first driving operation or a second driving operation, the second driving operation section requiring a shorter charging completion time to complete charging the main capacitor, than the first driving operation; and the first driving operation providing a higher charging efficiency than the second driving operation, the control circuit selecting the second driving operation when the finder eye contact detecting circuit detects athe eye contact with the finder, and selecting the first driving operation when the finder eye contact detecting circuit does not detect the eye contact with the finder.
The above and other objects, features, and advantages of the present invention will be apparent from the following specification and drawings.